The basic communication network in Bluetooth networks is called a Piconet. The channel access in a Piconet is managed by a Master which is one of the participants in the communication. All other participants in the communication are called Slaves. A master is allowed to serve at most 7 slaves, and a Master can be a Slave in another Piconet. A Slave can also be a Slave in another Piconet. A Master or a Slave that participates in multiple Piconets is called a bridge node and acts as a router between the Piconets. A connected network that spans more than one Piconet is called a Scatternet. Ad hoc multi-hop networks in Bluetooth networks are formed using Scatternets.
Multi hop communications are useful for extending the communication range of a device which is constrained by the maximum device capacity of a Bluetooth Piconet and/or user preferences. For example, a smart phone may prefer to communicate through its trusted laptop or PDA to the outside world. Hence in Bluetooth based ad hoc networks, having two devices within their nominal communication range is not a guarantee that they establish a direct link. This constrains the network topology.
Network topology has a great influence on the performance of the network. A casually designed network topology might be inefficient, and also might preclude some of the applications that otherwise could operate on the network.
Most of the network formation research for Bluetooth based ad hoc networks concentrates on finding an optimal initial topology for a scatternet.
One problem with static network formation protocols is that when a node moves and the topology changes, the initial criteria satisfied by the topology may no longer be valid.
Node mobility calls for a network topology optimization strategy as an integral part of mobility management and/or data traffic routing. This application takes the second approach and addresses the problem of network topology optimization while routing the data traffic.
Adapting the topology of a network based on the requirements of a data flow is known. “A Two-Phase Scatternet Formation Protocol for Bluetooth Wireless Personal Area Network”, Kawamoto, Y. et al, WCNC 2003—IEEE Wireless Communications and Networking Conference, vol. 3, 16-20 Mar. 2003, pages 1453-1458, discloses a two-phase scatternet formation protocol that supports dynamic topology changes. In a first phase, a control scatternet is constructed to support topology changes and route determination. The control scatternet does not operate according to the Bluetooth specification, but instead the piconets are synchronized so that there are common periods when a bridge node switches between piconets without informing the masters about the timing of each switch over. The second phase creates a separate on-demand scatternet whenever a source node wants to initiate data communications with another destination node. The on-demand scatternet formation is itself divided into two steps. In the first step, the control scatternet is used in the selection of a route in the control scatternet between a source and the master serving a destination. In the second step, the master node with which the source node communicates with selects the participating nodes for the on-demand scatternet. The master node uses its own slaves' and adjacent neighbor information to choose the participating nodes. Each master node must maintain all the information of its slaves and bridge nodes within its piconet and adjacent piconets. The on-demand scatternet is torn down when the data transmissions are finished. It will be appreciated that there is a heavy overhead in setting-up and maintaining the control scatternet and that the on-demand scatternet is used only as a temporary addition to the static control scatternet.